Why?
I've driven plenty and they all understeer.
In fact pretty much all cars understeer, its rather basic vehicle dynamics.
A car accelerating and turning will shift load to the rear, that will increase load and therefore grip at the rear and reduce load and therefore grip at the front. Result = Understeer.
Now the degree of understeer will vary from car to car, with the two main factors being the initial load over the front (more = less understeer and less = more understeer) and which end is driven (front = more work for the tyres and more oversteer).
Now depending on the car (and quite a few factors) you may be able to resolve this in two main ways. Either reduce the degree of steering applied and/or reduce the throttle, they both have the same end result, more grip to turn at the front and a reduction in understeer.
Now you can also (assuming the car is RWD) apply more throttle and if you have sufficient torque to get the rear tyres to a greater yaw rate than the front tyres you will transition to oversteer. However the Evora in question is not a powerhouse (current hot-hatches have more grunt - hell my Volvo produces more torque) and as such this should not be possible outside of 1st or 2nd and certainly not with TC switched on. Nor is this always the best option when going for out and out lap times, as you have to deal with both under and oversteer, all of which are working the tyres less effectively. Its almost always quicker to reduce understeer and get the tyres back to an optimum workload as quickly as possible. A place which occurs just as the tyres start to exceed the peak slip angle and self aligning torque has reduced.
So yes understeer is something you should associate with all cars, including Mid Engined ones.
Now the advantage on track of a MR is that is has a lower PMI than other layouts and will be less resistant to changes in direction, this can actually increase the speed and rate at which understeer will develop in the situation above, but it will also increase the speed and rate at which you can reduce it in the situations above. Making it highly adjustable, however it will also increase the speed and rate at which it will oversteer if you do something daft like lift off the throttle rapidly to try and fix understeer.
Its often confused that because the lower PMI makes a car react to direction changes more readily, that means its going to want to oversteer all the time, which is simply not the case. Its still bound by the four bits of rubber in each corner, the yaw rates they have, the load they have and the lat, long and rotational forces being applied to them that creates those yaw rates (and a lot of other factors due to rubber being really, really wierd stuff).
What GTS is allowing the Evora to do in power on oversteer with a moderate throttle application, with no noticeable understeer, in 4th and 5th gear, with TC switched on.
That's wrong.
I don't have the time to fully enjoy every title for its own good stuff. I want the best (what's possible) of everything put into one game! 
...one is aloud to have a dream, right?! 
Got promoted to C anyways.
